Revealing mistakes

When the main characters are tugging at the metal bars of the fence that has wrapped itself around the house, the bars bend too much to be made of regular metal - they look more like rubber, showing how it is merely a film prop rather than an actual fence.

At the end of the movie, the main characters escape the building inside which they have been trapped at what is supposed to be early dawn according to the storyline. However, the angle of the sun and shadows show that this scene was filmed closer to midday.